The introduction of low-cost global positioning system (GPS) units has given rise to a number of location-based services, particularly those that carry a database of points of interest by their map location. The database for an entire country can be stored in the unit and the information retrieved by map location, whether the unit is at that location or not. The database is contained in the GPS unit and may be updated periodically while the GPS unit is connected to an online service, for example, via the Internet while connected to a host computer.
Location-based information systems, however, position the actual data based on location so that notes, blogs, advertisements, and nearby people are made available as a location aware device traverses an area.
However, accurate location information can be difficult to acquire, particularly when in urban canyons or indoors, when using devices without GPS units, or without access to “war driving” databases, that is, a database of WiFi sites noting location by network.